The general objective of our proposed research is to characterize and compare dissipative processes that occur in the plane of composite membranes of human red cells and lamellar lipid systems. Transport phenomena in the plane of the membrane are limited by these dissipative processes, represented by coefficients of surface viscosity and surface diffusivity. With complex membrane materials such as the red cell membrane, dissipation rates are specific to the regime of material behavior being investigated, i.e., solid, semi-solid and liquid (plastic). The behavior of the material is characterized by viscoelastic recovery, "creep" and relaxation, and viscoplastic flow experiments. Dissipative behavior in these general material regimes will be studied as a function of temperature, and duration and magnitude of applied membrane forces. The transition from solid to liquid-like behavior in complex membranes is especially significant and represents permanent structural alteration or rearrangement which depends on molecular relaxation processes in the composite membrane. Simple membranes such as lamellar lipid systems (above the phase transition for ordered acyl chains) behave only as surface liquids. The state of the lipid membrane is altered by changes in temperature and surface density (produced by changes in membrane tension). Dissipation in lipid bilayers will be studied by measuring the changes in surface (lateral) diffusivity of specific membrane marker particles. Membranes forces and deformations will be produced using micromanipulation methods on human red cells and large lipid vesicles. The time dependent state of red cell membrane deformation and the fluorescence recovery of bleached fluorophores in lipid membranes will be used to determine the coefficients of surface viscosity and surface diffusivity, respectively.